I have a Sub Zro 690 S (M1971808) and the SERVICE light is flashing. I have unplugged it and restarted several times and it takes a while but eventually the service light returns. I already replaced the freezer thermistor and thought I had it solved because everything was fine for a few days.

But now it has come back slowly flashing again.

So I suspect I should replace the refrigerator thermistor as well (I did buy 2 of them) BUT I CANNOT FIND THE DAMN THING. I got the diagram but the schematic makes no sense to me. Can someone tell me in plain english what panels to remove and where to look for the frige thermistor.

AND is there anything else I might want to check that would be a 'usual suspect' for a flashing service light on a (approx) 2002 unit?

You'll need to remove all the ref side shelving, the light diffuser on top, and four phillips head screws that attach the evaporator cover to the back. Pull the top of the evap cover forward then up once it clears the contol panel and then out. There are two thermistors, one attached to the back wall and one screwed to the evaporator. Take a look at the evaporator, is it evenly frosted or is there a big chunk of ice on the upper left?

I see an evaporator replacement in your very near future, not a D-I-Y job by any stretch. Where are you located?

____________________"When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth." Sir Arthur Conan Doyle.

Samurai, There was no ice at all on the refrigerator evaporator. Since I only bought 2 thermistors before learing there were actually 3, I HAVE NOW REPLACED THE FREEZER AND THE EVAPORATOR thermistors. But not the one mounted to te back wall centered on the refrigerator section. My hope is that the ones I've replaced are the most likely to go out first (??) Is my grasshopper logic correct in that?

Nyet, tovarish. As Sublime Master AccApp indicated, you have the famous leaky evaporator that has been the bane of many Sub-Zero owners. Contact Sub-Zero and see what they'll cover on the repair for you. Usually, they'll cover the cost on the evaporator but you may have to pay for labor, depending on age and how hard you whine at them.

Limited 6th Through 12th Year Warranty
From the 6th through the 12th year from the date of original installation, your Sub-Zero warranty covers all parts that prove to be defective in materials or workmanship in the sealed system (parts only). The sealed system consists of the compressor, condenser, evaporator, drier and all connecting tubing.

There's actually four thermistors, and I have yet to see one fail. What happens is the connectors corrode and cause faulty responses to the control board. You can cut out the connectors and either use wire nuts, butt connectors, crimp connectors or solder to secure contact.

Is the ref side holding temp? How clean is the condenser? Is the condenser fan running?

____________________"When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth." Sir Arthur Conan Doyle.

A) Is there a sequence to use on the error code readout that would identify the problem as the Evaporator?

OR

B) If I remove the back panel and let the system run for a few hours will I then be able to observe ice build-up or whathaveyou that might identify the problem (I'm assumign that by the time I take out the shelves and re-remove the back panel any ice buildup will have melted already)

I'm hoping to avoid a Sub Zero service call only to find out it's not the evaporator (warranty) and then I'll be liable to pay for the service call after I've already done so much to try and fix the Service flashing light by replacing 2 thermistors.

Condenser is spotlessly clean. Condenser fan is running. Refrigerator and freezer appear to be holding temperature. When I ran the temp diagnostics it showed the frige at 41 even though it's set for 37, BUT by that time I had had the door open for a while so who knows...

Should I look at the Evaporator again and see if it has any ice buildup now? How is it normally supposed to look if it is running fine?